1. Field of the Invention
This invention relates to a device for heating and fixing a toner image on a support member.
2. Description of the Prior Art
A device in which a toner image support member is pressure-held between and conveyed by two rollers at least one of which is heated, thereby fixing the toner image is known. Usually, rotational force transmitting means including a member such as a gear is connected to the shaft on one end of one of the two rollers. The rotational force generated by a source of force such as an electric motor is transmitted through the transmitting means to rotatively drive said shaft and accordingly the roller having said shaft. The other roller is usually provided so that it is rotated by the friction force between it and the rotatively driven roller. In any case, the heat possessed by the roller is partly taken by the rotational force transmitting means. Accordingly, the temperature at the end of this roller to which is connected the rotational force transmitting means becomes lower than the temperature at the other end of the roller. A temperature difference created between the opposite ends of the roller results in a diameter difference between the opposite ends which is attributable to a thermal expansion amount difference. This causes a difference in pressure between the two rollers and between the opposite ends thereof. If such a difference becomes great, the toner image support member is wrinkled or moves obliquely or meanders and may be caught by various members provided along the conveyance path, thus resulting in jam or the like. Particularly, where the toner image support member is a long footage of continuous sheet used with a device for printing out the output of an electronic computer, a great temperature difference between the opposite ends of the roller causes the sheet to be laterally displaced from its regular path in the station for imparting the toner image to the continuous sheet (the position upstream of the fixing device with respect to the sheet conveyance) to laterally offset the position of the toner image imparted onto the sheet and in an extreme case, there occurs an inconvenience that the continuous sheet is severed. The long footage of continuous sheet is usually severed when it is laterally displaced by 1 mm or more from a predetermined conveyance path.